Centrifugal separator

ABSTRACT

A liquid component separated in a centrifugal rotor is thrown therefrom into a surrounding housing where the level of the liquid component is controlled by an element responsive to changes in such level and operable to regulate the supply of a superatmospheric pressure gas to the interior of the housing, the latter having a bottom outlet for discharging the liquid component and which is subjected to a counterpressure.

[ mmssz Feb, 8, 1972 References Cited [54] CENTRIFUGAL SEPARATOR [72] Inventor: Henri: Wilhelm Thyletors, Stockholm, rr STATES PA'IENTS Sweden [73] Assignee: Alia-Laval AB, Tumba, Sweden 958,770 5/1910 Richardson............................. 1,050,622 1/1913 Raasloffet al.... 1,723,329 8/1929 Chadbum..... 2,526,292 10/1950 221 Filed: Oct. 13,1969

2]] Appl.No.: 865,798

Primary Examiner-Jordan Franklin Assistant Examiner-George H. Krizmanich Attorney-Davis, Hoxie, Faitl'it'ull & l-lapgood [30] Foreign Appiication Priority Data Oct. 14, 1968 Swedenm.............................13806/68 therefrom into a surrounding housing where the level of the liquid component is controlled by an element responsive to changes in such level and operable to regulate the supply of a superatmospheric pressure gas to the interior of the housing, the latter having a bottom outlet for discharging the liquid A% A mu U lA 3% 0 mm lnu a 3 3W ,U 2.42 "0 me u 93 633 "R2 ml m Md" -l" m0" mBm Lml o W d S M UmF .11.] 218 555 [[1 component and which is subjected to a counterpressure.

4 Claims, 1 Drawing Figure CENTRIFUGAL SEPARATOR THE DISCLOSURE The present invention relates to centrifugal separators of the type in which the centrifugal rotor is surrounded by a stationary housing into which a liquid component of the mixture to be separated is thrown from the rotor.

In centrifugal separators of the above-noted type, it is known to provide the driving shaft of the centrifugal rotor with a pump rotor which pumps away the liquid component collected in the housing. Such a pump has certain drawbacks, among which are that it requires a high-pumping effect and also is eroded to a great extent if the pumped liquid com ponent is a sludge. Moreover, air is mixed into the pumped liquid, which is normally undesirable for various reasons.

An object of the present invention is to provide a centrifugal separator of the type described which avoids the above-noted drawbacks.

According to the invention, the interior of the stationary housing is provided with a level control means for the liquid component, such control means being arranged to regulate a supply of superatmospheric pressure gas to the interior of the housing, and the latter is provided with a bottom outlet for discharging the liquid component and which is subjected to a counterpressure. With this arrangement, the liquid cornponent thrown from the rotor into the housing is pressed by the superatmospheric pressure in the interior of the housing through a liquid seal having a substantially constant liquid level, maintained by the level control means, and through the discharge outlet to a desired destination, such as a container or a subsequent separator. After a condition of balanced operation has been reached, superatmospheric pressure gas may be supplied to the interior of the housing to replace such gas as has leaked from the housing or has accompanied separated components discharged from the separator. This means that the separator rotor itself serves as the pump for the component discharging through the outlet at the bottom of the housing, in that the latter component as it leaves the rotor will displace gas within the housing, and the resulting compression of the gas therein forces a corresponding quantity by volume of the component through the outlet at the bottom of the housing. The discharge takes place without an eroding effect, even if the component consists of sludge. Moreover, gas has an opportunity of separating from the component in the liquid seal formed by the component in the lower part of the housmg.

The invention may be used to particular advantage in connection with a nozzle centrifuge in which, in order to obtain sludge which is satisfactorily concentrated, sludge thrown from the rotor nozzles is returned to the inlet of the rotor through a pipeline leading from the bottom of the housing, the returned sludge usually being supplied directly to the vicinity of the nozzles in the rotor. ln a nozzle centrifuge having such a sludge return, the problems in regard to erosion and/or air admixture are often difficult to overcome.

Due to the superatmospheric pressure maintained in the interior of the housing, it is necessary to seal the interior of the rotor against the atmosphere in the interior of the housing. According to a preferred embodiment of the present invention, a paring disc provides an outlet for discharging a separated component from the rotor and forms a liquid seal between the atmosphere surrounding the rotor and an atmosphere present within the rotor. However, in order to prevent the latter atmosphere from increasing to a pressure which prevents entrance into the rotor of the mixture to be separated (or possibly the component which is returned to the rotor inlet), a communication is provided between the atmosphere within the rotor and the atmosphere surrounding the housing.

The invention is described more in detail below, reference being bad to the accompanying drawing in which the single illustration is a vertical sectional view of an embodiment of the new centrifuge chosen by way of example.

The centrifuge as illustrated comprises a rotor body i having a cover 2 secured to the rotor body by a threaded locking ring 3. The rotor is mounted on and driven by a vertical shaft 4 and is surrounded by a stationary housing 5. The bottom of the housing is sealed against the driving shaft 4 by a carbon ring 6 surrounding the shaft and urged against the rotor bottom by a spring 6a, the ring and spring being located in a guide 6b in the bottom of the housing 5. The rotor 1 contains a distributor 7 and a conical disc set 8, the latter being located as usual in the separating chamber of the rotor. Sludge outlet nozzles 9 are provided in the outer periphery of the rotor body. A supply pipe 10 for the mixture to be separated opens into the distributor 7. Liquid separated from the mixture and discharging from the inner edge of the disc set 8 passes through openings 11 to a paring chamber 12 in the upper part of the rotor, where this liquid forms a liquid level 14 on both sides of a paring disc 13, the separated liquid being pumped by the paring disc through a discharge pipeline l5.

Sludge discharged from the rotor nozzles 9 collects in the lower part of housing 5 where it forms a liquid level 16, the sludge being discharged through an outlet 17 extending from the bottom of the housing. Part of the sludge discharging through the outlet 17 is directed into a pipeline 19 by means of a controllable valve 18. The pipelines 10, 15 and 19 as well as the paring disc 13 are stationary, and these pipelines have respective depending portions arranged concentrically within each other at the top of the rotor. The outside of pipeline 15 is hermetically sealed against the housing 5, as shown at 15a. Also, suitable seals are provided where the pipeline l9 enters the pipeline 10 and where the latter enters the pipeline 15. The pipeline 19 opens into a space 20 below a conical disc 21 in the rotor, and from space 20 the returned sludge enters a number of radially arranged bent pipes 22 which lead the sludge outwardly to the vicinity of the nozzles 9.

A float 23 is provided in the interior of housing 5 and operates through a conventional float valve 23a to control admission of compressed air into the housing from a supply pipe 24. The latter may thus be considered as a source of superatmospheric pressure gas.

With this arrangement, as long as the counterpressure in the outlet 17 is constant, the pressure of the atmosphere within the housing 5 is kept constant.

The atmosphere in the rotor space 20 communicates with the atmosphere in the paring chamber 12 by way of the central air space 26 in the rotor. The rotor space 20 also communicates with the atmosphere surrounding the housing 5 by way of a central channel 25 in the driving shaft 4, this channel opening laterally through the shaft as shown at 25a.

in the operation of the centrifuge as illustrated, valve 18 is adjusted so that a desired part of the separated sludge is returned to the interior of the rotor in the vicinity of its nozzles 9. This adjustment creates in the outlet 17 a certain counterpressure which, in a condition of balanced operation, is maintained substantially constant. If the level 16 sinks in housing 5, the float valve 23-23a throttles the admission of compressed air from the pipe 24. This causes the pressure of the atmosphere in the interior of housing 5 to decrease, since the rate of compressed air admission from the pipe 24 will now be less than the rate at which air leaks from the interior of the housing (due to normal leakage). This reduction of pressure within the housing results in a reduced rate of discharge of the liquid component through the outlet 17, whereby the level 16 rises to the desired equilibrium position. Conversely, if the level i6 rises above the desired equilibrium position, the float valve 23-23a increases the rate at which compressed air enters the housing from pipe 24, and the resulting pressure increase in the housing causes an increase in the liquid discharge rate through the outlet l7, thereby lowering the level 16 to the equilibrium position.

i claim:

1. In a centrifugal separator for a mixture including a liquid component, the combination of a stationary housing, a centrifugal rotor surrounded by the housing and having an inlet for said mixture, the rotor also having an outlet from which said liquid component of the mixture is thrown into the interior of said housing, the housing having a bottom outlet for discharging said liquid component and which is subjected to a counterpressure, said housing being adapted to accumulate a body of the liquid component having a level, and means for controlling said level of the liquid component in the housing, said level control means including a source of superatmospheric pressure gas, and an element responsive to changes in said level for controlling a supply of gas from said source into the housing.

2. The combination according to claim 1, comprising also a nozzle forming the rotor outlet for said liquid component, the

combination comprising also a pipeline leading from the bottom of said housing for returning sludge from said nozzle to said inlet of the rotor.

3 The combination according to claim 1, comprising also a paring disc forming an outlet for a separated component of said mixture, said disc forming a liquid seal between the atmosphere surrounding the rotor and an atmosphere present within the rotor.

4. The combination according to claim 3, comprising also means forming a passage through which the atmosphere present within the rotor communicates with the atmosphere surrounding said housing. 

1. In a centrifugal separator for a mixture including a liquid component, the combination of a stationary housing, a centrifugal rotor surrounded by the housing and having an inlet for said mixture, the rotor also having an outlet from which said liquid component of the mixture is thrown into the interior of said housing, the housing having a bottom outlet for discharging said liquid component and which is subjected to a counterpressure, said housing being adapted to accumulate a body of the liquid component having a level, and means for controlling said level of the liquid component in the housing, said level control means including a source of superatmospheric pressure gas, and an element responsive to changes in said level for controlling a supply of gas from said source into the housing.
 2. The combination according to claim 1, comprising also a nozzle forming the rotor outlet for said liquid component, the combination comprising also a pipeline leading from the bottom of said housing for returning sludge from said nozzle to said inlet of the rotor.
 3. The combination according to claim 1, comprising also a paring disc forming an outlet for a separated component of said mixture, said disc forming a liquid seal between the atmosphere surrounding the rotor and an atmosphere present within the rotor.
 4. The combination according to claim 3, comprising also means forming a passage through which the atmosphere present within the rotor communicates with the atmosphere surrounding said housing. 